An object to be observed by a microscope is mainly divided into two categories, in which one is an amplitude object and the other is a phase object. Since the amplitude object varies brightness or colors thereof, the variation can be detected as a contrast by an eye or an imaging device such as a CCD. On the other hand, since a phase object only varies phase of light, it shows a poor contrast and hardly distinguishable as it is. Accordingly, there has been proposed various methods for changing phase variation of a phase object into discernible variation in contrast such as Japanese Patent Application Laid-Open No. 11-95174.
However, in examples disclosed in Japanese Patent Application Laid-Open No. 11-95174, in order to make phase variation of a phase object discernible variation in contrast, a light source is limited to a coherent light source.